1. Field of the Invention
The present invention relates to a shutter device and an imaging apparatus including a shutter device.
2. Description of the Related Art
An imaging apparatus includes a viewfinder that enables a user to confirm an image of an object captured by an image sensor. The operation by an imaging apparatus that displays an object image on a liquid crystal display (LCD) device or a comparable monitor is generally referred to as “live view” function. The following is a shutter device used in a conventional imaging apparatus.
A conventional shutter device includes two arms configured to form a parallel link mechanism capable of rotatably holding a plurality of blade groups. The shutter device includes a first-curtain blade group and a second-curtain blade group mounted on a shutter ground plate. In an exposure operation, the first-curtain blade group increases an aperture of the shutter from a closed state to an opened state, and the second-curtain blade group reduces the aperture from the opened state to the closed state.
The first-curtain blade group is connected to a first-curtain driving lever that includes a driving source (e.g., a spring) causing blades to travel and an armature magnetically attracted to a first-curtain holding electromagnet. In a shooting preparation state, a charge lever causes the armature to abut a yoke attraction surface of the first-curtain holding electromagnet and the first-curtain blade group is held in a shutter closing state.
The second-curtain blade group is connected to a second-curtain driving lever having an arrangement similar to that of the first-curtain driving lever. In the shooting preparation state, the charge lever causes the armature to abut a yoke attraction surface of a second-curtain holding electromagnet to hold the aperture in an opened state.
After a release operation, the charge lever retreats from a blade holding position. Both the first-curtain blade group and the second-curtain blade group are held at their start positions by the respective holding electromagnets. Both the first-curtain and second-curtain holding electromagnets generate magnetic force when electric power is supplied.
First, the imaging apparatus stops electric power supply to the first-curtain holding electromagnet to cause the first-curtain blade group to open the aperture. Then, after a predetermined time has elapsed, the imaging apparatus stops electric power supply to the second-curtain holding electromagnet to cause the second-curtain blade group to close the aperture.
In this manner, the shutter device exposes an imaging screen to light from an object based on a preset exposure time (i.e., shutter speed). After the second-curtain blade group completes traveling, the charge lever causes the first-curtain blade group and the second-curtain blade group to move toward their shooting preparation positions and wait for another shooting operation.
The sequence performed by a conventional shutter device having the above-described arrangement is generally referred to as “ordinary shooting.” As discussed in Japanese Patent Application Laid-Open No. 2006-98908, an imaging apparatus can be configured to hold a second-curtain driving lever with a member other than the second-curtain holding electromagnet when the imaging apparatus operates in a live view function mode.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 11-194394, a shutter device for an imaging apparatus can include a motor that rotates a charge lever connected to the motor in a predetermined direction to perform charge and release operations for a blade group.
Furthermore, as discussed in Japanese Patent Application Laid-Open No. 11-41523, a single-lens reflex imaging apparatus can perform an imaging operation with a combination of a focal plane shutter and an electronic shutter (hereinafter, referred to as “hybrid shutter”). In the imaging apparatus, a mechanical shutter constitutes a second curtain. The electronic shutter performs reset scanning for pixels of an image sensor prior to traveling of the second curtain. The reset scanning (processing for storing electric charge) for an image sensor is performed according to a scanning pattern corresponding to traveling characteristics of the mechanical shutter constituting the second curtain.
An imaging apparatus equipped with the above-described conventional shutter device needs to keep an aperture of the shutter in an opened state when the imaging apparatus operates in a live view function mode. In other words, the imaging apparatus continuously supplies electric power to the second-curtain holding electromagnet and, as a result, continuously consumes electric power.
An imaging apparatus equipped with the shutter device discussed in Japanese Patent Application Laid-Open No. 2006-98908 does not supply electric power to the second-curtain holding electromagnet when the imaging apparatus operates in a live view function mode. However, in this state, the second-curtain holding electromagnet is separated from the armature. Therefore, if the operation of the imaging apparatus shifts from the live view function mode into the hybrid shutter shooting mode discussed in Japanese Patent Application Laid-Open No. 11-41523, the imaging apparatus simultaneously performs charge and release operations for the first-curtain driving lever and the second-curtain driving lever. Accordingly, the time lag in the release operation becomes longer if the imaging apparatus shifts from the operation in the live view function mode into the hybrid shutter shooting mode.
Furthermore, an imaging apparatus equipped with the shutter device discussed in Japanese Patent Application Laid-Open No. 11-194394 does not supply electric power to the second-curtain holding electromagnet when the imaging apparatus operates in the live view function mode. However, Japanese Patent Application Laid-Open No. 11-194394 mentions nothing about a desired relationship between a mirror driving mechanism and a shutter driving mechanism to reduce the release time lag when the operation mode of an imaging apparatus is switched from the live view function mode to the hybrid shutter shooting mode.